Tuesday, 25 September 2007

Single jabs

These are images that we just can't see enough of in my opinion. They are from the Health Protection Agency's Centre for Infections, and show the uptake of measles and MMR vaccines against the incidence of measles infections and deaths.

Measles is a serious infection (mortality 1:5,000), is very contagious and it is unpleasant with fever, a rash, conjunctivitis, cough and cold symptoms, but there are a number of potential complications. Poor nutrition in the developing world, and immunocompromise in the West make these even more likely and thus infection more dangerous. Children in the UK with cancer who come into contact with measles are at a very high risk of complications.

Complications include ear infections (10%), pneumonia (5%), febrile convulsions (seizures which can be caused by any infection, and usually do not lead to epilepsy; 1:200) and myocarditis. About 1:1,000 of measles cases result in encephalitis with 15% mortality and serious long term complications in 40% of survivors such as seizures, deafness, paralysis, and learning disability

Subacute sclerosing panencephalitis is a rare illness that develops many years after infection by measles when very young (under 2yrs; 1:8,000) where persistent virus in the nervous tissue causes progressive brain damage, dementia, and death

Fortunately we can see that the rate of measles infection is now very low, and the number of deaths thus very small due to a concerted vaccination campaign using first single measles vaccine, and then MMR. Unfortunately it looks like people have forgotten how bad measles can be - the steadily climbing rate of vaccination has been compromised by the MMR-autism scare and measles is back.

This has lead some to argue that single vaccines should be provided. Leaving aside the obvious point that the MMR doesn't cause autism or gut problems, and that the vaccine was introduced to replace a single measles vaccine (Urabe) with undesirable side effects (meningitis), there are real problems with this idea. Separate vaccines must be administered many weeks apart (the minimum necessary period is unknown) to avoid interactions that might reduce the efficacy of the vaccines (the MMR components have been tested and shown not to have a problem if they are administered all at the same time), but they must also be given twice - to ensure coverage when very young (the first dose at 13 months), but also boosted to last for longer when older (the second dose before 5yrs of age). This gives 6 injections rather than two, and evidence suggests that parents are just much poorer at ensuring their children receive all the vaccinations. There is also a much longer period where children are not covered for those diseases they have not yet been vaccinated against. Note the increase in vaccine coverage following introduction of the MMR.

Side effects of the MMR are rare, and usually only after the first dose. These are milder versions of the results of infection, and thus much less common than with full infection, and due to the vaccine comprising attenuated viruses that replicate in the body. The most common side effect is a mild malaise, fever or rash after about a week, which resolves in a few days. Parotid swelling can occur in about 1% of children. Febrile convulsions can occur in 1:1,000 children (these do not lead to any long-term consequences such as epilepsy). Encephalitis is a theoretical risk but research suggests that MMR does not lead to any increased incidence. Very rarely clotting problems can occur in less than 1:20,000 children, and this resolves spontaneously.

Some people argue that only the measles vaccine should be given, but this underestimates the seriousness of mumps and rubella.

We can see from this graph that mumps is also massively on the rise, although this is presently in older children who have never been vaccinated. Mumps causes a fever and malaise with swelling of the parotid glands. Hearing loss is usually transient following infection, with deafness in only 1:20,000, but signs of meningitis are present in about 10% and encephalitis is found in 1:1,000. Pancreatitis is a potentially serious complication found in less than 10% of children. Orchitis (inflammation of the testicle) is very rare in children (but not adults), and almost never results in infertility because it is usually unilateral.

Rubella (german measles) is usually mild, with a low fever and rash for a few days. Complications such as arthritis, encephalitis or myocarditis are rare. However, maternal rubella infection can lead to severe damage to the foetus. Before 8wks gestation most children will be born with deafness, congenital heart disease, and cataracts. Infection at 13-16wks and infection will lead to impaired hearing in around a third of children (past 18wks damage is minimal).

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